1. Field of the Invention
Exemplary aspects of the present invention relate to a cleaning blade in image forming apparatuses such as printers, facsimiles, and copiers. The present invention also relates to an image forming apparatus, a process cartridge, and an image forming method using the cleaning blade.
2. Discussion of the Background
In electrophotography, a toner image may be formed on an image bearing member such as a photoreceptor and is subsequently transferred onto a transfer paper or an intermediate transfer member. Some toner particles may remain on a surface of the image bearing member without being transferred. Such residual toner particles are typically removed by a cleaning device.
Cleaning devices employing a rectangular-shape cleaning blade are widely used because of its simple configuration and cleaning ability. Such rectangular-shape cleaning blades are typically made of elastic bodies such as polyurethane rubbers. Typically, a base end of a cleaning blade is supported by a support member, and a leading edge is pressed against a circumferential surface of an image bearing member so that the cleaning blade banks up and scrapes off residual toner particles remaining on the image bearing member.
To improve image quality, small-size and spherical toners which can be manufactured by polymerization methods (such toners are hereinafter referred to as polymerization toners) can be used for image forming apparatuses. Advantageously, polymerization toners can be more effectively transferred from an image bearing member onto a transfer paper or an intermediate transfer member compared to pulverization toners. In other words, polymerization toners have higher transfer efficiency than pulverization toners. On the other hand, polymerization toners may be difficult to remove from a surface of an image bearing member by a cleaning blade because they may pass through a thin gap formed between the cleaning blade and the image bearing member because of their small size and spherical shape.
To prevent such passing through of toner particles, a cleaning blade is preferably pressed against an image bearing member with high pressure. However, as illustrated in FIG. 1A, a leading edge 262c of a related art cleaning blade 262 tends to curl up towards an adjacent surface 262b because the cleaning blade 262 is stretched in a direction of movement of an image bearing member 23 due to a friction force between the image bearing member 23 and the cleaning blade 262. When the cleaning blade 262 returns to its original shape, noise may occur. If the cleaning blade 262 continues removing toner particles with the leading edge 262c curling up, a leading surface 262a may be partially abraded, as illustrated in FIG. 1B. Eventually the leading edge 262c may be removed, as illustrated in FIG. 1C. Therefore, the related art cleaning blade 262 makes it difficult to remove residual toner particles.
Japanese Patent No. 3602898, for example, discloses a cleaning blade made of a polyurethane elastomer in which a part (hereinafter “contact part”) which is to be brought into contact with an image bearing member is covered with a surface layer containing a resin having a pencil hardness of from B to 6H. It is described therein that because such a surface layer is harder than rubber materials, the friction coefficient of the contact part is decreased, which results in an improvement of abrasion resistance of the cleaning blade. It is further described therein that the surface layer decreases a friction force between the image bearing member and the cleaning blade, which results in prevention of curling up of a leading edge of the cleaning blade. It is further described therein that the surface layer having a pencil hardness of from B to 6H is unlikely to deform, which also results in prevention of curling up of a leading edge of the cleaning blade.
Unexamined Japanese Patent Application Publication No. 2004-233818, for example, discloses a cleaning blade formed by the following method. First, an elastic blade is impregnated with an ultraviolet hardening material containing silicon and is subsequently exposed to an ultraviolet ray so that a hardened layer is formed on a surface of the blade. It is described therein that the hardened layer thus formed from the ultraviolet hardening material has a greater hardness than the elastic blade, and therefore abrasion resistance improves and curling up of a leading edge of the blade is prevented.